I agree that it is worthwhile to review and understand what luck does and how it affects skills so players can choose whether to level it or not. For me and the way I play however, it is indeed unimportant.
All the skills my character wants to use will get to 100. The luck bonus does no good at that point, so at my character's top level (which is what I build for), luck becomes unimportant. So, rather than spending a slot bumping an attribute by +1 that becomes unimportant later, I would prefer to use that attribute gain slot at level ups to push +5's to an attribute that I consider important. In my case, since I will not level beyond 20, I only have 19 level ups to build attributes - so each level up really has to count. To me, luck represents an 'oportunity lost' investment that may help early on, but would become useless to me later. Ymmv of course.
So, I don't care about trying to build diminishing skill bonuses. And of course, I don't care about Mehrune's
Butterknife Razor or betting in the Arena.
Those who want that early skill bonus and/or have the flexibility that going to high character levels (+45) provides may well consider luck.